No, I am talking rather about this optional solder bridge marked with AMP on the PCB:
With respect to the noise, I hear the following:
There is little that can be done about the first source apart from redesigning the PCB and perhaps replacing certain capacitors with more expensive tantalum variants.
As for the second source, I am wondering if we are dealing here with an undocumented audible brown out (i.e. undervoltage) warning. I am using the optional 850mAh battery and I charged my device well before use. By consequence, I do not hear it that often, only when manipulating the USB cable when connected.
However, those using the bottom plate battery of a mere 150mAh battery, perhaps without properly charging it, might here the high tone more often or even continuously.
I am hoping more users and certainly the designers will chime in here (pun intended) to clarify this situation.
According to the data sheet (in Chinese language only by the way),
if the load current drops below 45mA during 32 seconds, the IP5306 goes into standby.
This is useful information for making some sort of heartbeat circuit to keep the IP5306 from going into standby.
This is a hardware problem of the IP5306 buck converter going into standby after 32 seconds.
It is explained in this thread:
@jimit Over here in Europe, metric M3 screws are pretty easy to come by. However, I can imagine this to be more difficult in the US.
Since, I have the optional 850mA battery module installed, it requires slightly longer screws. From what I recall, 20mm length was just not long enough. Hence, I think 25mm length is what I need. I still need to make the trip to the hardware store, though.